(1) Field of the Invention
The present invention relates to a sequence program edit system for editing a sequence program displayed on a screen, and more specifically, to a sequence program edit system for editing a sequence program displayed by an SFC system.
(2) Description of the Related Art
In general, sequence programs to be executed by a programmable controller (PC) are expressed by many formats such as logic descriptions, ladder diagrams and the like. Among them, flowcharting is advantageous as it makes an overall flow of work easy to understand. A sequential function chart (SFC) system is available as one of the flowcharting. The SFC system represents a process to be executed in each step by various types of graphic elements such as transition, step and the like and expresses the overall flow by the combination of the graphic elements. However, a program representative of a specific operation in each step is created by logic descriptions, ladder diagrams and the like.
A sequence program of the SFC system can be created in such a manner that a plurality of blocks are formed by virtually partitioning a display screen into rows and columns and a graphic element is inputted by a software key after a cursor is placed on the desired block. When another graphic element is desired to be inserted vertically between graphic elements which have already been inputted, a cursor is positioned on the desired block and the desired graphic element is inserted therein. All the graphic elements below the row of the inserted graphic element are shifted downward by one block, and at the same time blanks are automatically inserted into all the blocks in the same row of the inserted graphic element to keep a balance as a whole.
However, since the blocks in the same row other than the block into which the graphic element has been inserted are inherently connected to the upper and lower blocks through any graphic elements, if these blocks are made blank, the flow of a program is cut off. To cope with this problem, a graphic of a vertical connector line has been conventionally inserted by an operator through a key operation into the blocks where the blanks were inserted. Thus, when there are many blocks into which the graphic must be inserted, a time-consuming job is required and a working efficiency is lowered.